Radio frequency transponder for use with a medium

ABSTRACT

A radio frequency transponder for use with a disc, such as a CD or DVD has an antenna formed by depositing a conductive solution on a surface of disc outside at adjacent to its outer periphery outside of the disc storage area to yield at least one conductive region. A transponder circuit is coupled to the antenna for supplying an RF signal to the antenna in response to a signal received from the antenna.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit, under 35 U.S.C. §365 ofInternational Application PCT/US2006/031736 filed Aug. 14, 2006, whichwas published in accordance with PCT Article 21(2) on Jan. 10, 2008 inEnglish and claims priority of U.S. Provisional Application No.60/817,751 filed Jun. 30, 2006, the teachings of which are hereinincorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates to the combination of a radio frequency antennaand a transponder circuit for use on storage medium, such as a digitalvideo disc (DVD) or computer disc (CD).

BACKGROUND ART

Many industrial and commercial electronic article surveillanceapplications make use of a radio frequency transponder for detecting andidentifying an article of interest. A typical radio frequency (RF)transponder for use in such applications comprises an antenna coupled toan electronic circuit carried on a substrate. In response to aninterrogation signal received by the antenna, the electronic circuitgenerates a response transmitted by the antenna for receipt at a basestation. The presence and characteristics of the response signalindicate the presence and nature, respectively, of the article thatcarries the RF transponder.

RF transponders of the type described above have proliferated in theretail environment for use in theft detection. Many different types ofarticles presently carry a transponder circuit which a store clerk willdeactivate after purchase by the customer. However, should someone tryand remove steal the article without purchase (and deactivation of thetransponder), the transponder on the article will respond to a signalfrom a theft detection system. The response from the RF transponder onthe article causes the theft detection system to generate an alarm sothat store security can apprehend the would-be thief before leaving thestore. Because of the effectiveness of RF transponders for theftdetection, many large retailers now require their vendors to providesuch transponders on articles for sale.

Presently, RF transponders of the type used for article surveillanceexist in various forms. One popular type of transponder comprises anadhesive tag that includes the antenna and circuit in a single packagefor adhering to an article. Other arrangements include a separateantenna, usually in the form of a thin conductive Mylar® film glued orotherwise attached to the article, for connection to a smallsemiconductor chip containing the transponder circuit. Unfortunately, RFtransponders of the type currently available are not well suited forcertain kinds of articles, especially CD and DVD discs. Adhesivetag-type RF transponder circuits, when attached to the top surface of aCD or DVD disc can upset the overall disc balance during use. Moreover,placing an adhesive tag-type RF transponder on the top surface of a discwill detract from the artwork printed on the disc. Also, placing thistype of RF transponder on the top surface of a CD or DVD so as to beentirely visible readily increases the likelihood that a would-be thiefwill attempt to disable the RF transponder to facilitate disc theft.

Another type of RF transponder currently marketed for use with CD andDVDs consists of a pair of half-circular conductive Mylar® arcs glued tothe periphery of the disc for attachment at opposing ends to a chipcontaining a transponder circuit. This arrangement suffers from severaldisadvantages. First, the cost of this type of RF transponder relativeto the cost of the manufacture of the disc is significant, making thistype of transponder expensive, if not cost prohibitive. Second, applyingeach of the Mylar® arcs to the disc will likely prove difficult in aconventional disc manufacturing environment.

Thus, there is need for a RF transponder especially suited for use on adisc such as a DVD or CD.

BRIEF SUMMARY OF THE INVENTION

Briefly, in accordance with the present principles, there is provided aRF transponder circuit for use on a storage medium, such as a disc(e.g., a CD or DVD for example). The RF transponder comprises an antennaformed by depositing a conductive solution on a surface of the discoutside of the storage region to yield at least one conductive portioncapable of receiving and radiating RF energy. A transponder circuit iscoupled to the antenna for supplying an RF signal to the antenna inresponse to a signal received at the antenna, such as from an externalbase station.

Providing the antenna outside the storage region, typically in thenon-metallized annular region of a CD or DVD disc, affords the advantageof enabling more reliable reading each of a plurality of discs in astack which has heretofore been difficult when the antenna lies insidethe storage region on the disc.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 illustrates a front view in perspective of a disc embodying an RFtransponder in accordance with a preferred embodiment of the invention;

FIG. 2 illustrates a top view of the disc of FIG. 1;

FIG. 3 illustrates simplified disc structure used for simulatingradiation patterns for the RF transponder of FIG. 1;

FIG. 4 illustrates a simulated pattern of the radiation expected to beemitted by RF transponder of FIG. 1 when incorporated in the discstructure of FIG. 3 in the absence of aluminum on the middle layer; and

FIG. 5 illustrates a simulated pattern of the radiation expected to beemitted by RF transponder of FIG. 1 when incorporated in the discstructure of FIG. 3 in the presence of aluminum on the middle layer.

DETAILED DESCRIPTION

FIGS. 1 and 2 illustrate a front view in perspective, and a top view,respectively, of a storage medium 10 embodying an RF transponder 12(best seen in FIG. 2) in accordance with a preferred embodiment of thepresent principles. The storage medium 10 illustratively takes the formof an optical disc such as a CD or DVD comprised of one or more annularsubstrates 14, each having a recorded layer 16 formed on a major surfacein spaced relationship with the recorded layer on the other substrate.Each substrate 14 typically comprises a layer of plastic formed byinjection molding to create a pattern of pits (not shown) in one of itsmajor surfaces. A metal coating, typically aluminum or an alloy of oneor more metals such as gold, silver, copper, zinc, and aluminum forexample covers the pits on each substrate, thereby forming the recordlayer 16. The arrangement of the metal coated pits defines the datacarried on the corresponding substrate 14. In practice, themetallization forming the record layer 16 on each substrate lies outsideof an annular region 20 that surrounds an opening 22 at the center ofeach substrate. The metallization of each record layer 16 extends justshort of the periphery of its associated substrate 14 so as to leave anon-metallized region adjacent to periphery of each substrate, asillustrated by the non-metallized region 24 shown in FIG. 2 adjacent tothe periphery of the upper-most substrate 14.

An adhesive/spacer layer 25 serves to attach the substrates 14 inface-to-face relationship with each other to yield the disc 10 such thatthe record layers 16 both face the same direction (e.g., downward inFIG. 1). The opening 22 in each substrate 14 facilitates alignment withthe other substrate. Moreover, the opening 22 can receive a spindle (notshown) to enable stacking of a plurality of discs for storage andhandling.

As best illustrated in FIG. 2, the RF transponder 12 comprises thecombination of an antenna 26 coupled to a transponder circuit 28. Thetransponder circuit 28 typically takes the form of a semiconductor chipor the like which contains various components which in combinationenable the chip to receive an RF signal via the antenna 26 and inresponse, generate a RF signal radiated by the antenna. The constructionand operation of the transponder circuit 26 is well known.

In the illustrative embodiment of FIG. 2, the antenna 26 comprises aconductive solution deposited on the non-metallized region 24 of theupper surface 30 of the disc 10, (i.e., the upper surface of the uppersubstrate 14), that that normally carries the artwork or other indiciaidentifying the disc (not shown). In the preferred embodiment, theantenna 26 takes the form of a dipole having opposed radiators formed bydepositing the conductive solution in two strips adjacent to theperiphery of the disc. While other types of antennas are possible, theuse of a dipole simplifies disc construction.

Typically, the conductive solution used to form the antenna 26 comprisesa conductive ink printed on the upper surface 30 of the disc 10,typically in conjunction with printing the artwork and/or otherdescriptive indicia on that surface. For example, the antenna 26 couldcomprise a layer of silver formed by printing a silver ink comprised ofsilver particles suspended in a solvent. Once the solvent dries, thesilver particles will form a conductive layer for receiving andtransmitting RF signals. Other types of conductive inks or conductivematerials, such as a conductive gel could also serve to form the antenna26.

Forming the antenna on the upper disc surface 30 during printing of theartwork on the disc 10 serves to minimize the number of manufacturingoperations needed, to create the disc 10 with the embodied RFtransponder 12. Moreover, the equipment (not shown) that serves to printthe artwork on the disc can readily be adapted to print the antenna 26.Using the same equipment to print the antenna 26 also helps reducemanufacturing costs.

Forming the antenna 26 by depositing a conductive solution on thenon-metallized region 24 so that the antenna lies outside the storagearea on the disc 10 (i.e., the antenna lies outside the metallization oneach of the record layers 16) affords a distinct advantage in terms ofthe ability transponder circuit 26 to receive and transmit signals. Asdiscussed in greater detail below, the metal coating forming each recordlayer 16 will adversely affect RF signals received by and transmittedfrom the antenna 26. Locating the antenna 26 within the area occupied bythe record layer 16 on each substrate (i.e., the data storage area) hasbeen found to adversely impact antenna radiation as compared to locatingthe antenna within the non-metallized region 24. Thus, locating theantenna 26 outside of the data storage area allows for better signalreception by and from the transponder 12, thus allowing signal receptionby and from the transponder 12 on each of a plurality of discs 10stacked adjacent to each other.

To appreciate the affect the affect that metallization can have on theantenna a simulation was performed using a three-layer disc structure100 of FIG. 3 composed of a pair of polycarbonate layers 102 and 104,respectively separated by an aluminum layer of 106. Each of thepolycarbonate layers 102 and 104 has an outer diameter of 120 mm andthickness of 0.6 mm, with the material properties of the polycarbonatebeing such that Er=2.8 and Tan delta=e⁻⁴. The aluminum layer 106 has athickness of 50 nm and a conductivity of 38000000 Siemens/meter. Thedisc structure 100 of FIG. 3 includes a transponder (not shown) of thetype described in FIGS. 1 and 2, with its antenna formed of a conductivesolution deposited on the upper surface of the upper polycarbonate layer102 so as to lie outside (to the left) of the left-hand most edge of thealuminum layer 106.

FIG. 4 depicts a radiation pattern for the antenna of the transpondercarried by the disc structure 100 of FIG. 3 in the absence of thealuminum layer 106 for a frequency of 0.91 GHz. As can be appreciatedfrom FIG. 4, in the absence of the aluminum layer 10, the antenna oftransponder carried by the disc structure of FIG. 3 exhibit radiationpattern consistent with a that exhibited by a classical dipole antenna.

FIG. 5 depicts the radiation pattern for the antenna of the transpondercarried by the disc structure 100 of FIG. 3 with the aluminum layer 106present. In comparison to the radiation pattern of FIG. 4, the radiationpattern of FIG. 5 shows some distortion due to the presence of thealuminum layer, despite the location of the antenna of the transponderoutside of the aluminum layer. Much greater distortion would be expectedif the antenna of the transponder were placed within the area of thealuminum layer 106, thus suggesting that if an antenna of transponderwere located within the metallized storage area of a DVD or CD,transponder performance would be greatly impacted.

The foregoing describes a RF transponder for use in combination with astorage medium such as a CD or DVD.

The invention claimed is:
 1. A method of providing a radio frequency(RF) transponder circuit on a medium containing a storage area withmetallization, comprising the steps of: forming an antenna on the mediumby depositing a conductive solution on a surface of a non-metallizedregion of the medium both outside of the storage area and adjacent to anoutermost periphery of the medium to yield at least one conductiveregion, wherein the forming is performed in conjunction with printing,on said surface, at least one of artwork and descriptive indicia; andcoupling a transponder circuit to the antenna for supplying an RF signalto the antenna in response to a signal received from the antenna.
 2. Themethod according to claim 1 wherein the medium comprises one of a CD orDVD.
 3. The method according to claim 1 wherein step of forming theantenna further comprises printing a conductive ink.
 4. The methodaccording to claim 3 wherein the conductive ink contains silver.
 5. Themethod according to claim 1, wherein the forming of the antenna isperformed by depositing the conductive solution using screen printing.6. The method according to claim 1, further comprising forming theantenna during the printing of the at least one of artwork anddescriptive indicia.
 7. The method according to claim 1, furthercomprising forming the antenna using an equipment that is same as thatfor the printing of at least one of artwork and descriptive indicia.